Light emitting diode (LED) provides many advantages such as longer lifespan, less power consumption, higher illumination and more eco-friendly materials. With advance of LED fabrication process and lower cost thereof, LED is not only adopted on traffic lights or indication lights of electric appliances, it also can be used on environmental decoration or lighting fixtures. As application scope of the LED lamps has been greatly expanded, they have to pass various official and authorized safety regulation tests before being marketed. Those safety regulation tests include insulation test at higher voltages and aging test at higher temperatures. The insulation test usually is performed at varying positions under a higher voltage to determine whether the insulation structure and internal electronic elements of the light bulb can withstand the high voltage without being pierced. Thus only having excellent insulation capability can pass such insulation test. The aging test is to dispose the light bulb in an environment with a temperature range from 90° C. to −25° C. for dozens of days to withstand temperature variations while torsional force is applied to the light bulb via a machine (such as the torsional force for turning the lamp shell). Such the aging test aims to check whether the coupling among the composed elements of the light bulb is firm enough. The lamp shell generally is bonded to an insulation base or heat sink through adhesive. Although there are various types of the adhesive, those with better heat-resistant capability usually have weaker adhesion force, while those with stronger adhesion force often are deficient in heat-resistance. Thus most adhesive cannot provide both strong adhesion force and great heat-resistant capability. Moreover, it is a severe test for most adhesive to be tested in the environment with temperature variations from 90° C. to −25° C. for dozens of days while the tersional force is constantly applied to.
R.O.C. patent No. M379021 entitled “LED light bulb” discloses an LED light bulb that includes a lamp cap, a lamp shell, an LED driving circuit board held in the lamp shell, a heat dissipation bracket, an LED and a coupling ring located on the heat dissipation bracket and a glass shade. It recites in its specification that “ . . . the spherical glass shade has an the annular neck boned to a teeth-shaped flank on the inner rim of the corresponding coupling ring through silicone . . . ”. Hence the glass shade in this prior art is bonded to the coupling ring through the silicone.
R.O.C. publication No. 201020465 entitled “Spherical LED lamp and method of manufacturing the same” discloses that a base is wrapped in an inflated foam tape before being inserted into a neck portion of a sphere. After the foam tape is inflated, it can provide anchoring and cooling effect. While this prior art has listed many possible embodiments for materials of the foam, it is not sure whether those materials can pass the severe high temperature test.
Since the glass lamp shade has a smoother edge, it is afraid that using the adhesive to bond the glass lamp shade to the lamp base or heat sink is difficult to pass the high temperature test. However, although using multi-layer or multi-material adhesive to hold the lamp shade might increase the chance to pass the safety regulation tests, the production cost also increases.